1. Field of the Invention
The present invention relates to a vehicular mobile Internet protocol (VMIPv6) based on Internet Protocol version 6 (IPv6) in vehicular wireless networks, and more particularly to a lossless handover method in vehicular wireless networks, which is capable of reducing a handover delay by continuously maintaining an original Care-of-Address (CoA) at road-sections even though an Access Router (AR) is changed and reducing overhead caused by duplicate address detection (DAD) by performing the DAD as a background process to confirm whether a new CoA is duplicated while performing communication using the original CoA at intersections.
2. Description of the Related Art
In recent years, with the increasing demand on applications such as traffic surveillance, traffic congestion control, vehicle location and navigation, electronic toll collection, mobility and infortainment, the interests in Vehicular Wireless Networks and Vehicular Intelligent Transportation Systems (V-Winet/V-ITS) are growing fast.
In V-Winet/V-ITS, drivers in a vehicle may use broadband wireless technologies for seamless interactive and intelligent services via vehicle to vehicle or vehicle to infrastructure communications. One of the main challenges in V-WINET/V-ITS is to support seamless streaming services such as traffic, news, travel, shopping, and even video and music by supporting fast and robust handovers between roadside wireless access networks. Furthermore, the core network of the roadside wireless access networks is evolving into an all-IP based network.
Accordingly, Mobile IPv6 (MIPv6) has become a global mobility solution of the Internet Engineering Task Force (IETF) that provides host mobility management. However, the long handover latency and the packet loss problem of MIPv6 depreciates Quality-of-Service (QoS) for multimedia service applications.
To reduce the handover latency and solve the packet loss problem in the MIPv6, the fast handover for the MIPv6 (FMIPv6) was proposed by IETF. FMIPv6 tries to reduce the address resolution time through address pre-configuration, i.e., it provides the fast IP connectivity as soon as a new link is established by predicting the handover and conducting the DAD procedure prior to the Layer-2 handover.
However, the vehicle's connection time to the roadside access router is shorter in V-Winet/V-ITS compared with that of the general MN (Mobile Node) in cellular networks due to the fast moving speed of the vehicles. Moreover, the FMIPv6 is not robust for multimedia streaming especially in V-Winet/V-ITS. In FMIPv6, a vehicle is pre-configured with only one new Care-of Addresses (nCoA) before it is attached to the new link. Therefore, this address pre-configuration is useless if the vehicle moves to a visiting network which is different from its handover predicition. In this case, FMIPv6 needs to take the full handover procedure of MIPv6, so the handover latency increases undesirably.
Some work has already tried to improve MIPv6 and FMIPv6. To achieve fast handovers in IPv6 mobility, Gogo et al. proposed the L3-driven fast handover mechanism using the abstract link layer information and primitives. It is independent of the link layer (L2) protocols and devices. Through the L2 primitives, the network layer (L3) can know the upcoming of L2 handover and L3 can prepare for the L3 handover in advance. As a result, the total handover delay is dramatically reduced.
The L2 handover means that a MN switches from the pAP (previous Access Point) to the nAP (new Access Point) and the L3 handover means that a MN switches from the pAR (previous Access Router) to the nAR (new Access Router).
To present an enhanced handover mechanism, Hsief et al. also utilize the additional primitives and parameters by newly adding them to the media independent handover (MIH) services defined in the IEEE 802.21. This scheme can reduce the handover latency by removing the router discovery time and design the network cost-effectively by reducing the coverage overlap between adjacent cells.
To eliminate the Duplicate Address Detection (DAD) delay, Leu and Mark and Campbell et al. proposed a fast handover mechanism using the fast neighbor discovery and the DAD for fast moving MNs. They modified the Neighbor Cache with a look up algorithm for a quicker DAD checking speed. Therefore, it solves the shortcomings of the conventional DAD when a router has more than two links.
The optimistic DAD (oDAD) eliminates the DAD delay based on the premise that DAD is far more likely to succeed than fail. To do this, an optimistic MN modifies the standard IPv6 operation rules while keeping backward interoperability. However, although this optimistic approach reduces the handover latency in non-collision cases, if an address collision occurs, it can incur some penalty to both an optimistic MN and a rightful owner of the address. Therefore, oDAD cannot be the unique solution for the DAD problem. Furthermore, since it is a complete end-to-end approach, only a MN can initiate the registration process with the new optimistic address.
To realize the fast vertical handover, Ishibashi et al. provide the virtual MAC address scheme. That is, to reduce the L3 handover, the virtual MAC address becomes a unique identifier for a MN within the Mobile Ethernet. However, this scheme has limits on implementation and needs the additional layer.
In order to support the real-time applications in Vehicular Ad-hoc Networks (VANETs), Maria Fazio and Mario Gerla proposed a Leader-based scheme that exploits the topology of VANETs and a distributed DHCP service to guarantee the fast and stable address configuration. However, it simply assumes the use of a DHCP server and suffers from the control message overhead problem since it is a proactive protocol. Additionally, it still needs the DAD when a vehicle changes the scope of its leader.
Qazi Bouland Mussabbir and Wenbing Yao optimized the handover procedure of FMIPv6 by using the IEEE 802.21 MIH services in VANETs. They introduced an “Information Element Container” to store the static and dynamic Layer 2 (L2) and Layer 3 (L3) information of neighboring access networks and proposed to use a special cache maintained by the vehicle/AR to reduce the anticipation time in FMIPv6, thus increasing the probability of the predictive mode of FMIPv6.
Jong Min Lee proposed a scheme called the global mobility management (GMM) for the inter-VANET handover of vehicles. The proposed scheme supports the fast handover process using the L2 triggering and the route optimization for packet transmission.
Chung-Ming Huang proposed the packet forwarding control (PFC) scheme in VANETs to select a common ahead point (CAP) as the tunnel source to forward packets. The CAP can forward packets to the pAR and the nAR with a short transmission path. During a vehicle handover, packets sent from the data center to vehicles can be forwarded through the CAP to the nAR directly without having to travel to the pAR. As a result, packets can be sent through a shorter delivery path during handover in the proposed PFC scheme. However, this scheme does not work if the CAP does not exist in the middle of ARs and can not reduce the number of DADs when the vehicle changes ARs.
Marc Bechler proposed MMIP6, a communication protocol that integrates multi-hop IPv6-based vehicular ad hoc networks into the Internet. While the existing approaches focus on small-scale ad hoc networking scenarios, MMIP6 is highly optimized for scalability and efficiency. However, MMIP6 is based on the principles of Mobile IPv4 and does not provide the interoperability with previous mobility schemes such as IPv6, FMIPv6 and HMIPv6.
Yuh-Shyan Chen proposed a NEMO protocol for VANETS. On a freeway, since every car is moving in a fixed direction with high moving speed, the car adopting this protocol can acquire an IP address from the VANET through vehicle to vehicle communications. The vehicle can rely on the assistance of the front vehicle in executing the pre-handover procedure or it may acquire its new IP address through multi-hop relays from the car on the lanes of the same or opposite direction and thus reduces the handover delay and maintains the connectivity to the Internet.
Todd Arnold also proposed the IP Passing Protocol to reduce the overhead of obtaining an IP address to under one-tenth of a second. This is done without modifying either the DHCP or the AP software. However, these previous schemes still do not satisfy the delay of the seamless services in V-Winet/V-ITS and consider the handover delay under the imperfect prediction of the vehicle and the out-of sequence problem.